There are many situations when it is desirable to improve the reliability of an RF amplifier through the use of parallel redundant circuits. In the simplest form, manual switching to remove the defective amplifier and replace it with a good one has been used for many years. For unattended systems, or systems where even brief shutdowns cannot be tolerated, automatic switching has been used. Unfortunately, rather complicated circuitry and components which may limit system reliability have been required.
This invention provides completely automatic switching of a much simpler type than have been employed in the past. Only a two-bit phase shifter and simple sampling-comparing circuit are required. Any pair or any single amplifier may fail with no change in output power.
In an unattended phased array radar, for example, using separate amplifiers in each of 32 antenna feed lines, several amplifiers (1-3) can fail without seriously reducing radiated (or received) power. These amplifiers are usually driven by a "single thread" amplifier from a power divider. Failure of this latter amplifier results in complete transmitter shutdown. The same concept will apply to a receiver chain with summing hybrids and "single thread" amplifier which must be made redundant by some means.